1. Field of the Invention
The present invention relates to a photosensitive polymer composition, to a method of using the composition for forming relief patterns, and to electronic parts. More precisely, it relates to a positive tone, heat-resistant photosensitive polymer composition capable of being converted into a heat-resistant polyimide polymer under heat, which is suitable for passivating films interlayer insulating films and others for electronic parts such as semiconductor devices, etc., to a method of using the composition for forming relief, pattern; and to electronic parts.
2. Description of the Related Art
Polyimides have good heat resistance and good mechanical properties, and are readily formed into films of which the surface could be well planarized. Having those advantages, they are widely used for passivating films, interlayer insulating films and others for semiconductor devices.
Where polyimides are used for passivating films or interlayer insulating films, the step of forming through-holes and the like in those films is achieved essentially in an etching process in which a positive tone photo-resist is used. However, the step comprises applying and removing such a photo-resist, by which the step is complicated. This is the problem with the step. For the purpose of rationalizing the working step, heat-resistant materials with photosensitivity have heretofore been studied.
Relative to photosensitive polyimide compositions, for example, known are (1) a polyimide precursor composition in which is introduced a photosensitive group through ester bonding (JP-B 52-30207, etc.), and (2) a composition as prepared by adding a compound that contains a carbon-carbon double bond capable of being dimerized or polymerized by the action of chemical rays, an amino group and an aromatic bisazide, to a polyamidic acid (JP-B 3-36861, etc.).
In use of such photosensitive polyimide compositions, in general, a solution of the composition is applied onto a substrate, then dried, and exposed to active rays via a mask, and thereafter the unexposed area is removed with a developer to form a pattern on the substrate.
However, the compositions (1) and (2) noted above are both negative tone ones, and the development for these requires an organic solvent. Therefore, when an etching process using a positive tone photo-resist is switched to a process using a negative tone photosensitive polyimide, the problem is that the mask for the exposure device and the development equipment must be changed.
On the other hand relative to positive tone photosensitive polyimides, for example, known are (3) a polyimide precursor in which is introduced an o-nitrobenzyl group through ester bonding (JP-A 60-37550), and (4) a composition comprising a phenolic hydroxyl group-having plyamidate and an o-quinonediazide compound (JP-A 4-204945).
However, the precursor (3) is essentially sensitive to light having a wavelength of not longer than 300 nm, and its sensitivity is low. Therefore, the precursor (3) is problematic in that an i-line stepper (for single wavelength light of 365 nm) which is much used these days in the art is hardly applicable thereto. On the other hand, the composition (4) is also problematic in that its sensitivity is still unsatisfactory even though higher than the sensitivity of the precursor (3). At present, no one could obtain positive tone photosensitive polyimides having satisfactorily good sensitivity.
The present invention is to overcome the problems noted above in the related art.
Specifically, the invention as herein described in one embodiment is to provide a positive tone photosensitive polymer composition having high sensitivity and capable of being formed into patterns having a good profile. In patterning the composition, the firm retention in the unexposed area is high.
In particular, the photosensitive polymer composition in certain preferred embodiments has extremely good heat resistance.
The invention as described in another embodiment is to provide a method of using the composition for forming relief patterns having a high resolution and having a good profile.
The invention as descriabed in a further embodiment is to provide electronic parts having fine relief patterns, in which the relief patterns formed have a good profile and which therefore have high reliability.
The photosensitive polymer composition of the invention comprises (a) a polymer soluble in an aqueous alkaline solution, (b) an o-quinonediazide compound, and (c) a dissolution inhibitor for the component (a) in an aqueous alkaline solution.
In the composition, preferably, the component (a) is a polyimide or its precursor soluble in an aqueous alkaline solution.
Also preferably, the component (a) is a polybenzoxazole precursor soluble in an aqueous alkaline solution.
Still preferably, the component (a) is a polyamic acid ester having repetitive units of a general formula (I): 
wherein R1 represents a tetravalent organic group; R2 represents a divalent organic group having a carboxyl group or a phenolic hydroxyl group; and two R3""s each independently represent a monovalent organic group.
Still preferably, the component (c) in the composition is any of onium salts, diaryl compounds or tetraalkylammonium salts.
Still preferably, the component (c) is any of diaryliodonium salts, diaryl sulfone compounds or tetramethylammonium halide compounds.
Still preferably the component (c) is a diaryliodonium salt of a general formula (II): 
wherein R4 and R5 each independently represent a monovalent organic group, and these R4 and R5 may be the same or different; m and n each independently represent an integer of from 0 to 5; and Xxe2x88x92 represents a counter anion.
Still preferably, the composition comprises from 5 to 100 parts by weight of the component (b) and from 0.01 to 30 parts by weight of the component (c), relative to 100 parts by weight of the component (a).
The method of the invention of using the photosensitive polymer composition for forming relief patterns comprises a step of applying the composition onto a substrate and drying it thereon, a step of exposing it, a step of developing it with an aqueous alkaline solution, and a step of heating it.
Preferably, in the method, the light to be used in the exposing step is of i-lines.
The electronic parts of the invention have the relief patterns as formed in the method noted above, in which the relief patterns act as a passivating film or an interlayer insulating film.